It's the same problem with VMWare Workstation Pro. API calls are appallingly slow. They take a full 3 seconds to execute, which is not even remotely close to acceptable.
To put this in perspective, this response delay would have been acceptable if the server were located on the moon (Earth–Moon–Earth communication - Wikipedia), but this is talking to localhost.
Sending vmrest 8 requests (on a dual core CPU), Windows taskmanager shows a high CPU load for vmrest.exe, so there's some very inefficient code running here. I never had this performance problem with VixCOM.